I own and use two of these bp2500 lights and I can say that it's very hard to accidentally touch the dimming switch. And the best way to adj is like you said with a meter and it definitely is full spectrum and only dimmable.The spectrum is non adjustable.
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To adjust the wattage get a kilowatt meter - they are cheap, plug it into mains, plug light into kilowatt meter and adjust the dimmer screw which is on the driver itself by the look of their picture.
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It says - prevent plant growth restriction by accidentally touching the dimming setting!
As clear as mud lol lol
I used a Luxmeter to get a reference.- How hard is it to adjust the power of the light or turn it down and is there a trick like a certain of degress to turn the switch thing?